Appendix A: Sources of Satellite Imagery

Satellite imagery

Several data capture techniques based on satellite and aerial
imagery were available at the time of publication. An overview of
the main techniques is provided below. It is expected that these
techniques will be revised and superseded with advances in
satellite technology, and therefore that this list should not be
considered exhaustive.

Optical Satellite Imagery (Thematic Mapper)

The Landsat series of satellites operates the Thematic Mapper
instrument. Unfortunately, the 30m pixel size has limited its
applications for individual peat slide investigations. However,
Landsat-7 now offers a 15m resolution panchromatic band which
enables mapping scales to 1:25,000. Furthermore the Indian,
IRS-1C
with 5m pixels improves mapping scales to 1:10,000. The IKONOS
satellite, available since early 2000, offers data which provides
1m ground resolution imagery and enables mapping scales of 1:2,000
or greater. The French
SPOT satellite provides 10m resolution
panchromatic data and the ability to acquire stereo image pairs. At
these scales individual flow lobes, ground fissures and subtle
morphology indicative of potential peat landslides may be
resolvable.

Microwave (Synthetic Aperture Radar Interferometry,
InSAR)

Radar imagery, at different wavelengths and polarisation, can be
obtained from both satellite and aircraft. Radar data can be
acquired during the night or day and effectively 'sees' through
cloud. Currently available
SAR (synthetic
aperture radar) data includes
ERS
with 25m spatial resolution,
RADARSAT
with 10-15m spatial resolution and stereo capability, and
JERS
with 18m spatial resolution. These data enable interpretation at a
range of scales from regional, to local and include vegetation
type, moisture content, debris sizes
etc. Synthetic Aperture Radar
Interferometry (
InSAR)
can create digital elevation model data and detect subtle changes
in elevation to the accuracy of the centimetre scale. This is
particularly useful for identifying changes in topography such as
subsidence and precursory ground movements on slopes.

Multispectral Video

Multi-spectral video cameras operate at the visible to near
infra-red portion of the spectrum and can be mounted on low-flying
aircraft. They can generate pixels of less than 1m ground
resolution and are therefore suitable for large mapping scales.
Field spectra obtained from in-situ measurements are used to
determine different classes of iron oxide precipitates from the air
and, by inference, the different pH levels of drainage systems.
This may be particularly useful for the mapping of peat landslide
groundwater systems.

Hyperspectral Scanners

Airborne hyperspectral scanners are much more complicated and
expensive instruments than multispectral video. They can be mounted
on low-flying aircraft. Remotely sensed multi-spectral data have
been shown to be of considerable use for landslide investigations.
Uses include the mapping of geological units in areas of poor
exposure through estimation of soil moisture content, the
estimation of soil thickness prone to landslides and the mapping of
geomorphological features of landslides at the regional scale and
the local scale.

Unmanned Aerial Vehicles (
UAVs)

UAVs (commonly
referred to as drones) are increasingly being used to provide site
specific high resolution photography and digital elevation data
(Hackney and Clayton, 2015). Good quality data acquisition is
reliant on accurate and precise ground control and careful survey
planning. In the
UK, the Civil Aviation
Authority (
CAA) define
operating regulations (
CAP393;
CAP722)
which constrain survey areas to within c. 500m 'line of sight' of
the operator and c. 400m altitude. A license is required to use
drone acquired data for commercial purposes.